things you cant do (not a complete list, just examples):
modify 3dmark's executable to give a different score
modify the saved result with a hex editor or similar before uploading
change 3dmark graphics settings so they are no longer at default

That's not all! You can still leave things to Lady Luck. From the pool of valid entries, we will randomly pick one person, who will bag an awesome new PowerColor Radeon HD 6870 X2 dual-GPU graphics card! So there's simply no reason not to try!

It is possible to run background 3D or any demanding apps alongside 3Dmark?? if yes, I would try ATITOOL, GPUTOOL, OCCT, a heavy WEBGL stuff, Furmark, Kombustor, and Prime95 if my computer doesn't ignite

One thing I noticed is that 3DMark 03 will say your drivers are not acceptable if you're running WDDM 1.1. WDDM 1.1 is all that is available for those using Vista/Win7 if you're using an older ATi card. I got my score submitted anyways. That had to be the longest 3dMark run I've ever done!